html,
body {
    height: 100%;
}

.wrap {
    min-height: 100%;
    height: 100%;
    background: url(../img/updating.jpg);
    background-size: cover;  //只支持IE9+  
    -webkit-background-size: cover; //webkit核心  
    -moz-background-size: cover; //FF核心  
    -o-background-size: cover; //应该是Opera核心吧，反正不是IE的，就先不管它了
    background-repeat: no-repeat;
    background-position: center;
}
